1. Field of the Invention
This invention relates the heat-shrinkable polymeric articles and their use.
2. Summary of the Prior Art
Heat-recoverable polymeric articles are well known in the art and heat-shrinkable articles have been extensively used for covering substrates, for example the ends of electrical cables and splices between electrical cables. Reference may be made, for example, to U.S. Pat. Nos. 2,027,692, 3,086,242, 3,243,211 and 3,396,455 the disclosures of which are incorporated by reference herein. When a hermetic seal is needed between the heat-recovered article and the substrate and/or the seal must withstand high separation forces, as for example when the substrate is a pressurised telephone cable, it is common practice to coat the interior surface of the heat-recoverable article with a layer of a fusible material such as a hot-melt adhesive or a mastic to improve the seal between the recovered article and the substrate. Heat-shrinkable articles having a solder insert have been extensively used to provide insulated soldered joints between electrical components. Recovery of heat-recoverable articles is usually effected by hot air or a flame. However, the combination of convection and conduction heating which these methods involve can be unsatisfactory when a fusible insert is employed, since the continued heating which is required to fuse the insert, after the article has recovered, can damage the article. This problem is considered in U.S. Pat. No. 3,396,455, which describes the use of infra-red radiation to heat a heat-shrinkable polymeric sleeve and a fusible insert, typically a solder insert, positioned within the sleeve, the sleeve transmitting a fraction of the infra-red radiation to the insert so that the insert is heated to its fusing temperature more rapidly than it would be if it was heated by convection and conduction; preferably the sleeve is heated to its recovery temperature before the insert reaches its fusing temperature.
One method of making a heat-recoverable article having a closed cross-section is by wrapping a sheet of heat-recoverable material around a substrate to be covered and securing the edges of the sheet together. A number of ways of securing the edges together have been disclosed, for example in U.S. Pat. Nos. 3,379,218 and 3,455,336, the disclosures of which are incorporated herein by reference.